The invention relates to a method of inspecting moving material, and though specifically directed to a process for inspecting a transparent web of glass of indeterminate length to detect flaws, contaminants, defects or similar foreign bodies thereon or therein as the transparent glass web is being manufactured by a conventional float glass process, the invention is equally applicable to inspecting individual transparent bodies, such as individual sheets of transparent glass, as well as opaque webs of indeterminate length, and/or individual opaque bodies. Thus, while the present invention is specifically directed to the manufacture of a transparent float glass web or sheet, the invention is equally applicable to the inspection of virtually any transparent or opaque product, including but not limited to opaque webs of tin plate, steel, aluminum foil or the like, virtually any type of transparent or opaque polymeric/copolymeric synthetic plastic films, individual sheets of glass or virtually any body upon or in which flaws or defects might reside. However, since the invention has been reduced to practice with respect to the inspection of float glass webs, the specification shall be primarily directed to the latter process without, of course, limitations upon the eventual products capable of being inspected for any of a variety of flaws or defects.
A glass inspection system associated with the production of float glass is disclosed in U.S. Pat. No. 4,492,477 in the name of Jacques F. Lesser granted on Jan. 8, 1985. This patent makes mention of the difficulty of distinguishing between glass defects and soil or foreign bodies present on the surface of a float glass sheet, and seeks to discriminate between flaws of the glass material itself, such a bubbles, drops, inclusions and projections of tin, for example, which effect the flatness and transparency of the glass, as opposed to simple dirt on the glass surface which can be washed away. The patent recognizes the conventionality of utilizing laser beams and infrared in conventional glass inspection systems, as well as the supposed disadvantages thereof, such as perfect synchronization, constant velocity, high cost of use, and high risk of deterioration. The patentee found that any flaws in the glass, be it bubbles, blow holes, drops or even partial inclusions, causes flatness defects on the glass surface. By illuminating the glass the deviation of the luminous rays caused by flaws renders the image thereof more luminous than the general image of the source of light. This deviation is attained by the effective of refraction in the mass of the deformed glass, and thus glass deformation as an overall defect can be distinguished from simple soiling. The inspection system includes a source of light located on one side of the sheet of glass and a photosensitive sensor located on an opposite side of the sheet of glass. A flaw causes a deviation of the beam of light which passes through the glass sheet to refract the light creating a bright image at the sensor which indicates the presence of a flaw, whereas soil or dirt simply causes the beam of light to darken. The inspection system also includes a plurality of light sources associated with a plurality of sensors for scanning sections of the glass with a slight overlap in adjacent scan areas. A camera is associated with each scan area and includes associated optics, photodiodes and circuitry to detect flaw signals which are subsequently compared with information stored in buffers for eventually cutting the glass to remove defects.
U.S. Pat. No. 5,157,266 granted on Oct. 20, 1992 to Roland Schmiedel discloses another method of inspecting transparent sheets or webs for the presence of defects, particularly enclosed core seeds, by utilizing a flying light spot. The flying light spot directs light through the glass web to a receiver which has transparent and opaque regions. When the light passes through a glass web which is free of defects, the light spot covers the transparent and opaque regions in a continuous alternating fashion of regular pulses, but any defects in the glass create a fluctuation in these pulses indicating the presence of a defect.
Another process for detecting the presence of defects on a moving sheet of glass is disclosed in U.S. Pat. No. 5,220,178 in the name of Mark J. Dreiling et al. granted on Jun. 15, 1993. Light from a light source passes through a dark (black) background slit and the glass sheet and is detected by a camera coupled to a computer. Speck defects and fisheye defects act as optical lenses and appear darker than the dark background and are thereby distinguishable.
In U.S. Pat. No. 3,533,706 in the name of Robert E. Maltby, Jr. et al. granted on Oct. 13, 1970 glass is inspected for defects by utilizing light rays passing through the glass and discriminating glass defects from dust and/or dirt and/or water by the angle of light deviation. A sensor produces a signal as a function of the intensity of the light which indicates the severity of the defect. Defects in the glass will scatter the light rays whereas if there are no defects in the glass the light rays will not be scattered, and the latter achieves the desired discrimination.
U.S. Pat. No. 4,461,570 in the name of Harry L. Task et al. granted on Jul. 24, 1984 and U.S. Pat. No. 4,647,197 in the name of Katsuhiki Kitaya et al. granted on Mar. 3, 1987 each disclose the utilization of a camera to inspect a transparent glass windshield by sighting through the windshield upon a target and determining the presence or absence of defects in the glass by the pulse generated from the target. Defective (distorted) glass will create a target pulse different from acceptable glass.